When planting with a conventional row crop planter having a plurality of row units mounted on a toolbar, it is necessary to provided a sufficient a down force on each row unit to ensure that the seed trench opener fully penetrates into the soil. To provide the necessary down force, each row unit is typically provided with a down force generator at the linkage mounting in the row unit to the toolbar. The down force generator may be a mechanical, spring type, generator that produces a fixed down force or which may provide for adjustment to vary the down force. Pneumatic or hydraulic down force generator's can also be used which facilitate electronic control of the magnitude of the down force. Proper down force control is also essential to provide the proper amount of soil compaction in the side walls of the seed trench.
In order to control the magnitude of the down force, it is necessary to measure the magnitude of the down force in real time during the planting operation. One method to measure of the down force is to provide a strain gage on a linkage used to support one of the ground engaging and load carrying the wheels of the row unit. Various a strain gage arrangements have been developed. One example is shown in patent application WO 2008/086283 A2. There, a load sensing pin, equipped with a strain gage, is used to mount the gauge wheel adjustment linkage. The down force is transmitted from the gauge wheel to the adjustment linkage and from there to the load sensing pin. A wiring harness then connects the load sensing pin to a controller, which is then interacts with an adjustable down force generator to produce the desired down force. The disadvantage of this load sensing pin it is the relatively high cost and necessity of a wiring harness.